Highly efficient standard circular polarizing filter for all cameras with beam splitters in the light paths of their TTL exposure meter and with autofocus lenses. Circular polarization has the same pictorial effect as linear polarization, but allows for proper exposure metering and/or autofocus distance settings.

Linear and circular polarizers both consist of a linear polarizer foil but differ in their construction in the following way. Modern SLR cameras have have a beam-splitting prism that sends part of the incoming light to the meter and part to the viewfinder. The effect is that the light entering the meter is partially polarized by the beam-splitter. A linear polarized placed on the lens of such a system will act as a second polarizer and block light to the meter by a degree dependent on the angle between the prism and the polarizer on the lens. The result is incorrect exposure/aperture values from the meter. The circular polarizer circumvents this problem through the addition of a 1/4-wave retarder, or delay, foil. This ensures that the linearly polarized light is changed into a rotation that appears unpolarized to the meter, resulting in proper exposure/aperture readings.

This filter uses our standard B+W F-Pro filter mount, which has a front accessory thread and is made of brass. Compared to the earlier standard mount introduced in 2001, the F-Pro mount has become thinner. Now it can be used with wide angle lenses, including most 24mm focal lengths on a full frame body, without vignetting. Another advantage of the F-Pro mount is it's modified retaining ring, which is no longer threaded in from the front, but holds the filter glass in place from the back. When removing a filter or lens hood that has been screwed on too tight to the filter, the retaining ring is not at risk of loosening.